Hydraulically operated control mechanism



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HYDRAULICALLY OPERATED CONTROL MECHAISM mw ww Patented Apr. 17, 1945 OPERATED CONTROL MECHANISM Gunnar A. Wahlmark, Rockford, lll.

Application August 1, 1942, Serial No. 453,207

19 claims. (ci. 121-41) HYDRAULICALLY It is the general object of the invention to provide a new and improved hydraulically operated control mechanism of the servo type. More particularly it is an object to provide a new and improved hydraulically operated control mechanism for adjusting the stroke of the pistons of piston type pumpsand motors. This application is a continuation in part of my copending application Serial No. 432,917, filed March 2, 1942.

Another object is to provide a yreversible wobbler type mechanism with a new and improved control means for adjusting the stroke of the'pistons, and the position of the wobbler on both sides of neutral as well as to its neutral or nostroke position.

Another object is to provide a new and improved servo type control operable in combination with a reversing valve to accomplish such result.

It is another object to provide such a mechanism with a unitarywobbler reversing and stroke adjusting control of the servo type, and more particularly to provide a unitary control of this kind of extremely small size, light weight and high sensitivity.

Another object is to provide a servo control mechanism embodying a rotary valve member having an edge operable as a valve, the invention contemplating modification of the contour of the edge of the valve member to vary the operating characteristics of the mechanism.

A further object is to provide a new and improved fluid actuated stroke control means for piston type pumps and motors, including mechanism for changing the stroke of the pistons, and which lends itself to modication to vary the time required to change the stroke.

Other objects will lbecome readily apparent from the following description, taken in connec' tion with the accompanying drawings, in which:

Fig. 1 is a front elevational view, partly in section along the line l-l of Fig. 2, of a preferred form of my invention.

Fig. 2 is an endvview, partly in section, along the line 2-2 of Fig. 1,

Fig. 3 is a fragmentary central longitudinal section along the line 3--3 of Fig. 2, with certain parts at the right hand end turned 90 about the shaft axis.

Fig. 4 is a fragmentary section along the .line 4-4 of Fig. 3.

Fig. 51s afragmentary View along the line 5-5 of Fig. 3.

Fig. '7 is a, vertical section along the'A line '1-1 of Fig. 3. s

Fig. 8 is a horizontal section along the line 8-8 of Fig. 7.

Fig. 9 is a horizontal section along the line 9 9 of Fig. '7.

Fig. 10 'is a diagrammatic representation of the hydraulic circuit for one piston pump device with its servo control valves and the wobbler adjusted to their neutral or no-stroke position.

Fig. 11 is a similar circuit diagram with the servo control valves and wobbler adjusted to their maximum stroke positions -for fluid discharge from the pump in one direction.

Fig. 12 is a similar circuit diagram with the servo control valves and wobbler adjusted to their maximum stroke positions for uid discharge from the pump in the opposite direction.

Fig. 13 is a similar circuit diagram with the servo control valvesmoved to their neutral position, the wobbler still remaining in the maximuml stroke position of Fig. 11.

Fig. 14 is a similar circuit diagram, with the pump wobbler in its no-stroke position and a modified form of servo control'adjusted to its neutral or no-stroke position.

Fig. 15 is a fragmentary sectional view along line 3 3 of Fig. 2 showing a second modified form of servo control.

Fig. 16 is a section along line lli-I6 of Fig. 15.

Fig. 17 is a fragmentary view along line n n of Fig. 16.

Fig. 18 is a circuit diagram, with the pump wobbler in its no-stroke position, of the modified form of servo control of Figs. 15 to 17.

Fig. 19 is a fragmentary view of some of the parts shown in Fig. 16 and with the servo valve in two different positions of adjustment.

There is illustrated in the drawings and hereinafter described in detail, a preferred form of the invention, together with a modification thereof, with the understanding that the disclosure is intended as an exemplcation of the principles of the invention and is not intended to limit the invention to the forms shown. The scope of the invention. will be pointed out in the appended claims. v v

In the form selected for purposes of disclosure and as illustrated in Figs. 1 to 13, the invention comprises generally a three-quarter horsepower 6000 R. P. M. direct current motor M, two twelve 'cylinder wobbler type piston pumpsP and P with self contained servo controls C and C', respectively, a g'ear type pump GP for furnishing a fluid (such as oil) for control and make-up purposes, reduction gearing G connecting the motor shaft M to a pump shaft S (which is common to both of the pumps P and P') ,high pressure safety valves V and V for the pumps P and P', respectively, and a casing or housing H which encloses and connects certain of the parts to provide a unitary structure. It is contemplated that the inlet and outlet ports for each pump will be connected by means of suitable conduits to a fluid motor (indicated at FM in Fig. which may be a rotary motor, a single piston and cylinder device or of any other desirable form.

More particularly, as illustrated in Figs. 1 to 9, the housing Hl has a lower portion forming a reservoir R 'for oil or other suitable fluid, and an upper portion 2|' forming a casing for the pump P'. A casing 22, for the motor M, is suitably secured to the left hand end (Fig. 1) of thelower portion of the housing H. The motor shaft M extends through an opening in the adjacent housing wall 23, through a mechanical seal 24 (which is shown as of the type disclosed and claimed in my Patent No. 2,216,218, dated October 1, 1940) and into a bore 25' in a pinion 25.

This pinion is formed integrally with a shaft 26 which is supported in a. bushing 2,1 carried in a lbracket-like extension 28 on the housing wall 23.

The fit of the motor shaft M in the bore 25' is such that the end ofthe motor shaft is supported in the pinion. A driving connection is provided by a. cross key 29 which extends through a diametrical slot in the shaft M' and into registering longitudinal slots (not shown) in the pinion 25.

The gear lpump GP (Fig. 1) comprises a pinion 30 pinned on the end of shaft 26 and a meshing pinion 3|, rotatably mounted on a pin 32. A chamber for the gears is formed by a recess in an extension 34 on the bushing 21, and a suitable cover plate 33. l

The gearing G (Figs. 1 and 3) for driving the pumps P and P includes the drive pinion 25, an idler gear 35,-and a gear 36 (Fig. 3) formed integrally with a cylindrical pump drive member 31 which is rotatably mounted in the upper'portion of the housing H by means of a ball bearing 38.

As illustrated herein the pumps P and P' (and their 4associated servo controls C and C) are substantiallyalike in construction and operation, so that a detailed description of pump P will Suiiice. The corresponding parts of pump P will be given the same numerals with a prime added thereto.

, ports 69 (in the valve plate 60) with an annular The shaft S for the pumps extends in opposite directions from the drive member 31 (Fig. 3) and has a central enlarged portion 4|) which is fitted into a central bore in the member 31. A plurality of pins 4| extend radially inward through bores in the drive member v31 and into registering sockets 42 in the shaft S to form a driving connection therebetween, a pair of bands 43 being provided to hold the pins 4| in their bores and sockets.

The pumps, as mentioned hereinbefore, are of the wobbler type and have tweleve cylinders each. Preferably theyv are of the type disclosed and claimed in my Patent No. 2,280,875, dated April 28, 1942. As illustrated, the pump P comprises a casing 2|, generally cylindrical in form as shown best in Fig. '7, and secured at one end t0 the casing 2|' of the pump P. A cylinder block 50 hastwelve cylinder bores 5| therein, and has an external flange 52 positioned against an annular shoulder 53 within the casing 2|.

Pistons 54 are reciprocably mounted in the cylinders 5| and extend therefrom and intoA engage- S by means of a pin 68. The wobbler plate is thus adjustable angularly about the pin 58 from the neutral or no-stroke position shown in Figs. 3 and 10 toward the full stroke positions shown in Figs. 1l and l2 for wobble plate 55.

A disk-like member or valve plate 60 is positioned in the pump casing against the flanged end of the cylinder block, and a cap member 6| is positioned against the outer surface of the valve plate 6|). The cylinder block, valve plate and cap member are effectively clamped in plac'e in the casing by a ring 62 which has external screw threads engaging corresponding threads on the casing 2|, and plurality of screw devices 63, herein twelve in number, which are threaded through the ring 62 and against the cap member 6| to tighten the parts vin place. This type of clamping means for the 'ports has the advantage of the full tensile strength ofthe casing as distinguished from prior constructions wherein bolts under tension were used, thescrews 63 herein being under compression.

The ow of fluid to and from the pump cylinders 5| is controlled by means of a wheel-like valve 65, which is positioned in a cylindrical valve chamber 66 formed in the cylinder block 50, and is 'driven by the shaft S through an eccentric pin 4(i1 thereon so as to have a gyratory motion. This type `of vvalve is disclosed and claimed in my Patent No. 2,190,812, dated February 20, 19410. Briefly, it includes a rim 68 which covers and uncovers the adjacent' ends of the cylinders 5i and alternately connects them to the valve chamber 66 outwardly of the rim 68 and inwardly of the rim. The outer portion of the. valve chamber connects through an annular series of port 10 in the cap member 6|, this annular port communicating in turn with a first pump port 1| (Fig. 2). A second pump port 'I2 connects with a recess 153 (Fig. 3) in the cap `member 6l, and 'through aplurality of ports 14 in the valve plate communicates with the gyratory valve 65 inwardly of the rim 68. Since the rim of the valve is connected t0l its Ahub 15 by spokes 16 communication is established periodically between the ports 14 and the cylinders 5l.

When the invention is used for pumping fluid at relatively high pressures, the valve 65 is preferably made relatively thin, as shown. The peripheral portion of the valve plate 60, and the portion just inwardly of the ports 69 are backed up rigidly by the cap member 6| as is evident from Fig. 3. To reinforce the center of the valve plate when the ports 14 are pressure or outlet ports, the chamber 13 is arranged so that the iiuidunder high pressure can act against the adjacent central portion of the valve plate and keep it in efficient sealing contact with the valve 65.

As illustrated herein, the shaft S is supported at its ends by bushings 18 and 18 which are mounted in the cylinder blocks 50 and 50' and have outwardly extending flanges which are clamped against'shoulders in the cylinder blocks `contemplated that the pump shaft S will be driven continuously by the motor M and that the `output of the pumps P and P' and the direction of flow of the fluid therefrom, will be controlled by adjustment of the wobble plates of the pumps vfrom neutral to forward and reverse positions. 'I'he means for'adjusting the wobble plates will now be described.

As illustrated in the drawings the adjusting means for-each pump comprises a control sleeve 85 (Fig. 3), control pistons 86 and `81- (Figs. 3 and 7) and means including the servo control C for controlling the fluid acting on the control sleeve and control pistons. The control sleeve 85 is slidably supported on thel cylinder block-50 and is provided with an internal annular shoulder 88 which functions as a piston. An annular chamber 89 surrounds the cylinder block between the shoulder piston 88 and anopposed shoulder 90 on the block 50. As more fully described hereinafter, the chamber 89 is supplied with fluid'from the gear pump GP to move the control sleeve towards the wobbler of the asso-l ciated pump and thereby determine the angular position of the wobbler. In Fig. 3, the control sleeve has moved the wobbler 55, 56 to a neutral or no-stroke position wherein the right hand end 9| of the control sleeve engages the outer mem` ber 55 of the wobbler throughout its periphery and holds it in exact neutral.

The control pistons 86 and 81 (Fig. 7) are herein arranged in pairs, the pistons 86 operating through'piston rods 96 (Figs. 3 and 7) to move the wobbler in one direction from its neuftral position (against the action of fluid on the control sleeve piston 88), and the pistons 81 op erating through piston rods'91 to move the wobbler in an opposite direction from neutral. Each pair of piston rods 95 are formed as the legs of a U shaped member, the bight 08 of which is pivoted in a lug 09 formed integrally with the inner wobbler member 56. Cylinders for the pistons 86 and cylinders |0| for the pistons 81 are bored through the drive member 31 and arel then closed at one end by means of plugs |02 and |03, respectively, the plugs being held in place by the pins 4|. may properly be referred to as forward and v reverse pistons'since their function, primarily,

The control pistons 86 and |11 (Fig. 8.) this fluid can be directed out through a valve port ||2 to a passage ||3 which leads ultimately to the contro1 cylinders |00. When in this position, fluid from the vcontrol cylinders |0| is exhausted through a passage or port ||4, through a port ||5 in the casing |05, a port ||6 in the valve RV and an axial passage ||1 in the valve which discharges at its lower end into the casing 2| of the pump P. Rotation of the valve RV in a clockwise direction from the positionV of Fig. 8 directs control fluid through a port ||8 in casing |05 into port ||4 and on to contro1 cylinders |0| while at the same time fluid from the control cylinders |00 exhausts through a passage ||3, a port ||9 in casing |05, valve port ||6 and passage ||1. A leakage groove |21 surrounds the valve RV and is connected to the return passage ||1 by a port |28.

.The servo valves SVF and SVR are connected to the reversing valve RV so as to be operated simultaneously therewith, the valve SVF functioning when the reversing valve is moved in one direction from neutral to a forward position (Fig. 11) and valve SVR functioning when the valve RV has been moved to its reverse" position valves. are cylindrical in form and-slide in parallel is to reverse the direction of fluid flow through teristic ofthe contro1 sleeve is utilized in a' unique manner in connection with the 'servo control C, the construction and-operation of which ,will n'ow` be described. v

The servo control designated generally by the letter yC is associated with the pump P and includes a cylindrical reversing valve RV and a pair of servo valves SVF and SVR (Figs. 3, /7 and 9). mounted in a bushing or`casing |05 supported in a vertical position in a-plate |06 secured to the top of the pump casing 2| by screws |04. This valve is herein provided with a stem |01 Ifor the attachment of an operating arm'IDB-and is adapted to be rotated out of the neutral position of Figs. 1 to 3 and 6 to l0 to the forward and reverse positions of Figs. 11 and 12, respectively.

As shown most clearly in Figs; 3, 'I and 8, con-- trol fluid under pressure supplied through a port ||`0 in the casing |05"enters a chamber in the casing formed by a "cutaway portion on the valve Y RV. By rotating. the valve counterclockwise The reversing valve RV is rotatably 1 bores |29 and |30 in a block or casing |3| which is mounted xedly on the control sleeve 85 and is secured thereto by screw devices |32 so that the casing for the servo valves moves with the contro1 sleeve 85 whose movement the servo valves control. As `shown in Figs. '1 and 9 the block |3| is guided lbetween parallel ways |33 formed on the pump casing 2|, to prevent rotary movement of the sleeve 85.

Although a more complete disclosure of the fluid circuits for the pumps and controls will be found in the circuit diagrams of .'Figs. 10 to 13, some of the passages are illustrated in Figs. 3, 4, 7 and 8. In these figures the passage ||3 includes (Fig. 3) connecting bores in the plate |06,

connecting bores in the casing 2|, connecting bores in the cylinder block 50, a port through bushing 18, an annular groove in the shaft S, a short radial port, a longitudinal bore (Fig. 4) and 'an oblique bore in the shaft, and a recess (Fig. 7)

in the member 31 which connects the outer end of the oblique bore with the two control cylinders |00. A corresponding series of bores, ports and recesses form the 'passage ||4.

The high pressure relief valves V nand Vfare alike so a description of valve V in connection with Fig. 2 will sufce. The pump ports 1| and r 12 are connected by a by-.pass port |45. A valve |46 -is arranged to control the lay-passing of fluid through this -port and is operable in this capacity when port 1| is the outlet port of the pump and also when the port 12 is alternatively the outlet port. Valve |46 has a cylindrical portion |41 which is slidably mounted in a bore in the valve Acasing |48 and is engaged by a coiled spring |49 -whic`h serves to urge'the valve |46 constantly tofluid discharged by the pump acts against the left hand end of va-lve |46, and when the pressure rises above the value for which the spring |49 is adjusted, valve 46 opens and by-passes fluid back to the port 1| which is then the inlet port for the pump. When the wobbler is reversed so that port 1| is the pump outlet port the fluid acts on the exposed surfaces of the valve |46 which are within the port 1|. These surfaces include the exposed end of the cylindrical portion |41 and part of both sides of the valve |46. The parts are so proportioned that the areas acted upon by the fluid to urge the valve |46 to its open position exceed the area acted upon by the fluid to seat the valve by an amount equal to the cross sectional area of port |45.

Thus the valve |46 opens to by-pass fluid at the same pre-adjusted pressure for both directions of pump discharge.

Reference is now made more particularly to Figs. 10 to 13. In these figures there is illustrated the hydraulic circuit for the pump P' and since the circuits for the two pumps are identical a 1| and 12' are shown connected to a suitable fluid motor FM' by means of conduits |50 and |5|. Fluid from the reservoir R is conducted to the gear pump GP' by a conduit |52 and is conducted away from the gear pump by a conduit |53' which leads to the port H0 of the reversing valve RV. maintain constant pressure in the conduit |53 and to permit excess fluid to pass back to the reservoir. A conduit |55 leads from the conduit |53' to the casing |56f of a pressure reducing valve PRV. Fluid which passes the valve PRV -is conducted b y a conduit |51' to the charmberBS' wherein it acts on the piston 88' formed on the control sleeve 85. The valve PRV' has a reduced cylindrical portion |58', which normallylies opposite valve ports |59' in the casing |56' so as to restrict the passage of fluid over the valve. The valve is urged into this position by a spring |60', a stem IBI on the valvel engaging a perforated disk |62' to limit the movement of the valve by the spring. The fluid in chamber 89' moves the control sleeve 85 towards the left (Fig. 10) to the no-stioke position shown since the pistons 86 and 8l' are then inactive.

The pressure of the fluid in chamber 89' is herein controlled by the servo valves SVF and SVR' by regulating the exhaust of fluid from said chamber through an exhaustpassage |65. This passage leads to a port |66. which communicates with bores |61' and |68' in which thev valves SVF and SVR' are slidable. Preferably the port |66' is so 4positioned that when the servo valves are in the positions shown in Fig. 10, there is a slight discharge of fluid into' the bores |61' and |b8, this fluid then returningto the reservoir R by gravity. The discharge under these conditions is small but it'does effect the pressure in the chamber 89' to the extent that valve PRV' is in haust passage |65 slightly open in neutral, then upon any kmovement of the valves SVF' and SVR' from neutral the exhaust of fluid from passage |65' increases instantaneously.

The reversing valve RV', when in the position shown in Fig. 10 opens slightly the ports l| I2' and I8' to the fluid supply in I', thus supplying fluid in small quantities tothe pistons 8G' and 81' and equaliaing the pressure thereon. Movement of the valve RV' 'in either direction from the posi- A by-pass valve |54 is provided to its restricted position of Fig. 10. With the ex'- passes from the supply conduit |53', through port H0', port ||2' and passage |I3 to cylinders |0|' to act on pistons 81'.. Simultaneously the servo valve SVR is pulled towards the right from the position shown in Fig. 10 so as to at first uncover the lower end of exhaust port |66' and thereby reduce the pressure in the annular control sleeve chamber 89', the exhaust of fluid through passage |65' then being greater than the fluid supplied through the ports |59 of the reducing valve PRV' due to the restriction caused by the port |58 of that valve. The pistons 8l' then exert a. force on the wobbler which overcomes the effect of the control sleeve piston 86'.

and the control sleeve is moved towards the right from the position of Fig. 10 towards the position of Fig. 11. Since the casing |3|' for the servo valves is carried on and moves with the controlsleeve the casing IBI follows the servo, valve SVR' to its right hand position (as in Fig.- 11) and until the port |66' is again Just slightly uncovered bythe end of the servo valve and the exhaust of fluid through passage |65 is substantially stopped. The pressure in cham.- ber 89' is then built up tothe full value required to counterbalance the effect of the pistons 8l. Since the servo valve SVR is mechanically coupled to the flange |20 of,the valve RV'v the position of the valve member SVR is determined by the angle through which the valve RV' is shifted, and this -position of the member SVR' will determine the extent of the movement of the casing |3|' as it follows" the servo valve SVR' just far enough to cause the port |66' to be covered by the end of the valve member SVR'. The control sleeve 86', being rigidly connected to the casing I3l', is thus arrested at anyselected position corresponding. ito the angle through which the valve RV' is shifted. The wobbler is thus adjusted to whatever position is selectedifor the servo'valve SVR', which may be anywhere between neutral and maximum stroke. ThusI the direction of movement of`the valve RV from neutral determines the direction of flow of the fluid from the pump GP' and the distance the valve RV' is moved from neutral determines the volumetric output of the pump.

In Fig. 12 the reversing valve RV is shown in its forward position, the servo valve SVF' then functioning to determine thev volumetric output of the pump and the pistons 86' acting to move the wobbler clockwise from its no-strike position to the position shown. i

In Fig. 13 there is illustrated the positions of the parts and the condition of the c'rcuit when the reversing valve RV' and the servo valves SVF and SVR' are moved quickly from their reverse positions of Fig.,11 to their neutral or no-strike positions of Fig. 10 and before the control sleeve 85' has had time to move to neutral in response thereto. -The exhaust port |66' is, therefore, entirely closed, preventing even the slight leakage which normally passes therethrough when the parts have reached equilibrium. This condition causes an increase in the ,pressure of the control fluid in chamber 89' and also in the right hand end of the casing |56' of the pressure reducing valve PRV' with the result that this valve is shifted to the left as shown in Fig. 13 and permits increased flow of fluid through the ports |59'. This causes a fast movement of the wobbler to its neutral position and provides for a rapid deceleration oi' thev associated motor FM'. Since the ports I|2' and ||8' are both slightly open to the fluid in chamber lll', iiuid can now-to the cylinders |88 and back from the cylinders to permit the wobbler to return to its neutral position.

Fig. 14 illustrates a form of theinvention embodying a modification of the Aservo control. In l this form, a single servo valve SVX' is used.v

This valve is connected by a link |15' and pivot pins |18' and |11 to a ange |18 on the reversing valve RV'.' 'The parts are arranged asvshown so that with the wobbler and the reversing valve in their neutral positions, the link is in a dead center position. 'I'hus regardless of the direction of movement of the reversing valve from neutral, the servo valve -SV X moves towards the right and opens the exhaust or relief port |88'. If the reversing valve is moved in a clockwise direction from the position shown in Fig. 14, con- ||8 and passage H4' to cylinders |88' and actuates the pistons 86' so that the wobble plate turns in a clockwise direction from the position'` vof,Fig. 14. Movement of the control'sleeve 85' then causes the valve casing |8I'" of the servo .ffvalve ISVX also to move towards the right, following the servo valve to the new position thereof. vCorrespondingly, if the reversing valve RV' is moved in a counterclockwise direction from the position of Fig. 14, control. uid from the port ||0' passes through port H2' and passage trol'uid passes from the port H0' through port v Preferably the plate |06 which supports the reversing valve RV and the associated servo valves SVF and SVR, is mountedso that it may be adjusted on the casing 2| longitudinally of the axis of the casing so as to permit of slight. adjusthaust port |86. One common way to obtain this adjustment is by enlarging or clon-gating the holes Vin |85 through which the clampingscrews |04 pass (see Figs. 8 and 9) so'that by loosening the screws the plate can be shifted to a slight extent. It is to bel understood that when the wobbler has been adjusted to a stroke producing position bv the actuating pistons 86', for example (Fig.

12). the force of these pistonson the wobbler is A rapid change in pump stroke causes an equally rapid acceleration or deceleration of the motor FM to which pump is connected.

In cases Where a slower acceleration or deceleration is desired, a slower change in pump output can be obtained by having the servo valves closed completely in neutral position and by providing relatively weaker springs |80 for the Valves PRV. This result is obtained with the form of the invention illustrated in Figs. 15 to 19.

Figs. 15 to 19 illustrate another modified form of part of the invention, the remainder of which is like that shown in Figs. 1 to 13. As shown in connection with a pump P, the control Asleeve 85 forms a member movably or slidably mounted on va support consisting of the cylinder block v5|). A means for actuating the sleeve 85 is found in the piston -formed by the annular shoulder 88 thereon, this piston being subject to the fluid in the chamber 88, the pressure or e'ect of which on the piston is governed bya servo valve SVY. As illustrated in Fig. 18,'uid from the pump GP is supplied to the chamber 89 through 'conduits and |51. A uid control port 88 communicates at one end with the chamber 89 and extends y radially through the control sleeve 85, partly radially and partly longitudinally in a valve casing member or block |8| which is secured by screws A|82 to and is carried by the sleeve 85, and then radially upwardly (Fig. 15) through a bushingl |83 which is slidable, radially of the shaft S, in

the casing member |8|. 'I'he block |8| is guided,

as shown in Fig. 7, between parallel shoulders |33 i on the casing 2| and thereby holds the sleeve 85 against rotation. The upper or outlet end |84 'y of the port |88 is at the outer'end of the bushing fluid therefrom through the port |80 while the ment of the servo valves with respect to the excounter-balanced by the force of the annular' control sleeve piston 88' and' the force which the pump pistons 54' exert against the wobbler during their discharge or exhaust strokes. When the load on the pump is heavy and the discharge pressure is relatively high, the force which must be exerted by the control sleeve piston 88is substantially less than when the load on the pump is light and its discharge pressure is relatively low. I'he force exerted by the pistons 85 is constant when these pistons are operable. When the force exerted by the pump pistons 54 goes down the force exerted by the control sleeve piston 88 must pressure and quantity of the fluid supplied to the chamber 89 from --the pump GP is governed by valves |54 and PRV. y i

A'valve SVY is herein provided yfor controlling the `valve port |84. This valve is somewhat in the form of a flat disk carried on and -rotatable with the stem |81 of the reversing valve RV. Herein, a hollow hub`| on the valve SVY extends into a'borel in the valve stem |81 and is secured thereto by a pin |9I. The under surface of the valve, as shown in Fig. 15, is at and rides over the upper end of the bushing 83 which is urged into sealing contact with the valve by a coiled 'spring |85. .The peripheral edge of the valve hasv a contour which is non-circular in form so that by rotating valve SVY the port |84 may be opened or closed As illustrated, the valve has a neutral position as shown in Figs. 16 and 18 in which a mid-peripheral portion |88 of the valve closes the port |84. The edge portions. |81

and |88 of the valve on each side of the mid-pory tion recede inwardly from a circle centered on the` axis of the valve stem |81 so that by rotating the valve SVY in either direction from itsneutral position the valve port I 84 is uncovered to permit discharge of fluid therefrom. This `permitsl of movement ofthe control sleeve towards the left (Figs. 15 and 18) under the inuence of the pistons 86 or 81 until the sleeve 85 has carried the casing member to the left far enough so as again to close the valve port |84. The valve usually, but Y not necessarily, is symmetrical with respect to a' line passing through the axis of the valve and the mid-peripheral portion |86.

Byv varying the contour of the valve portions |81 and |88 it is possible to vary the amount which the stroke of the pistons of pump P is changed for a given angular movement of the valve, and this in turn varies the speed at which a fluid motor FM, coupled to the pump, is operated.

In Fig. 19, the valve SVY is shown in fulllines in a partly opened position to which it has been moved, and before the casing member has had time to assume its corresponding position to close the valve port |84 again. The valve port |84 is thus shown partly open, to permit discharge of iluid therefrom and thereby lower .the pressure of the uid in chamber 89 so as to enable the wobbler actuating pistons 81 to move the wobbler to a new position. There is also shown in dotted lines, the position of. the valve SVY when moved quickly to its full stroke position and before the -casing |88 has followed to its new position. rIhe port |84 is then substantially wide open. This causes a marked drop in the pressure in chamber 89 which in turn permits the valve PRVjto move to its fluid restricting position, thus reducing the supply of iluid to chamber 89 and permitting rapid movement of the wobbler to its full stroke position. As the sleeve 85 moves towards the left and carries the casing member |8I with it (Figs. 15, 16 and 19) the valve port |84 is closed by the side portion |95 of the servo valve SVY since (looking at Fig. 19) the casing member |8| moves towards the left while theservo valve remains in the dotted line position.

In Fig. 18 the parts are shown in the positions assumed when the reversing valve RV and the wobbler 55, 56 are in their neutral position. The valve PRV is shown with a spring |60 of such strength that under this condition of pump operation the valve is in its wide open position. Since the valve port |84wis closed, the valve PRV (and also the annular piston 88 on the control sleeve 85) is subjected to the full pressure of the gear pump GP as determined by the by-pass valve |54. Upon movement of the reversing valve RV to a position corresponding to the full line position of the servo valve SVY in Fig. 19, the valve port |84 is opened and the pressure in chamber 89 is reduced, thus enabling the wobbler actuating pistons 81 to tilt the wobbler to its new position clockwise (Fig. 18) from the position shown. The new position of the wobbler is one wherein the valve port |84, moving with the control sleeve- 85, is again closed or almost; closed by the servo valve SVY. In practice the valve port |84 is actually left slightly open when the wobbler is in positions other than neutral. This slightly or so-called "cracked open` condition of the servo valve when out of its neutral vposition permits a continuous outlet of iluid from the chamber 88 and thereby relieves the-pressure therein to an lextent which varies with the load on the pump. y When the load on the pump P is heavy (i. e., the

, fluid in the cylinder bores is under high pressure during the discharge stroke of the pistons) on the control sleeve piston 88 can be relatively.

low to make up the force necessary to counter-` balance the force of the pistons 8l. Under ths condition the valve PRV is in its restricted position, If theload on the pump P is reduced so that the discharge pressure in the cylinder bores 5| drops, the force of the pump pistons 54 drops, in counteracting the force of the wobbler adjusting pistons 81, with the result that the control sleeve, shifts slightly in a stroke increasing direction. 'This movement of the control sleeve carries with it the valve port |84 and further closes that port. The pressure of the fluid in chamber 88 then rises and the valve PRV shifts towards its wide open position because of the rise in pressure o! the iluid acting on the annular piston 88.

The operation of the various forms of the invention Vis believed readily understood. With the motor M in operation, the pump GP, as well as the shaft S for the pumps P and P', is driven. In the forms shown the valves |54may beset to maintain a pressure such as 100 pounds per square inch inthe conduits |53 and |55, it being understood that although the operation of the pump P is independent of the pump P', a single pump GP supplies the control iluid for both piston pumps. With the form shown in Figsfl to 14 the valves PRV may be provided with springs operable to permit the valves to move to their open position when the pressure of the fluid in chamber 89 is about 80 per cent of the iiuid pressure in conduit |55. In these forms of the invention the servo valves are slightly open when in their neutral position and with the wobblers 4in neutral. In all forms of the invention there is a small opening of the reversing valves when in neutral, to supply uid to ports ||2 and |I8 and to equalize the pressure on the pistons 88 and 81.

In the form of the invention of Figs. 15 to 19,

wherein the servo valve closes the port |84 when in its neutral position the spring |80 for the valve PRV is p referably weaker than in the other forms, and may be selected to permit the valve to open when the pressure of the fluid in chamber 89 is 30, 40, 50, (or some,other) per cent oi the pressure of the uid in conduit |55. The strength of the springs for the valves PRV is selected to provide the desired speed in effecting changes in pump stroke. h 4

Upon moving a servo valve from its neutral position in Fig. 18, this form of the invention functions in a manner similar to that hereinbeforc described in connection with Figs. 10 to 13.

A distinct advantage of the invention as illustrated in Figs. 15 to 19 is in the form of the servo valve embodied in it. By changing the form or contour of this valve it is possible to vary the amount the stroke of the pump pistons is adjusted for a given angular movement ofthe servo valve. The valve is in eiect two valves in that one edge o! the valvefunctions in forward and the other in reverse positions thereof. The contour of the forward" valve portion could readily be dif- -ferent from the reverse valve portion. The

, servo valves together with the automatic control i for supplying lluid under pressure continuously to of the pressure o f the iluid by the PRV valves and the ease with which the valves may be modied in design provide a, highly advantageous and simple servo control mechanism.

I claim:

1. A fluid operated servo control mechanism for a movably mounted element having, in combination, reversing means for moving said element in opposite directions from a neutral position, a member movable in one direction from a neutral position and operable t'o control the position of said element on both sidesof its neutral position, means forming a control piston operable to move said member toward its neutral position, means said piston to move said member toward its neu- 'meansx and said device, a reversing valve movable l trai position. mechanism for controlling the pressure of the tluid acting on the control piston comprsing a pair of servo valves anda casing for the servo valves movable with said member," a reversing valve for controlling said reversing means,

and means connecting the servo valves to the reversing valve so that one servo valve operates for each direction of movement of said element.

`2. A fluid operated servo control mechanism for a movably mounted element having, in combination, means for moving said element in opposite directions from a neutral position, a member movable in one direction from a neutral position and operable to control the position of said Velement on both sides of its neutral position, means forming a piston operable .to move said member toward its neutral position, means for supplying limited quantities of fluid under pressure continuously to said piston to move said member toward its neutrall position, mechanism for controlling l, the exhaust of the iiuid acting on the control piston comprising apair of servo valves anda casing for a servo valve controlled port movable with said member, and a reversing valve foi' controlling said` rstmentioned means.

3. A fluid operated servo control mechanism for an element movable from a neutral position to selectable forward and reverse positions, having, in combination-fluid' operated means for moving said element out of its neutral position to forvice opposing the movement of said element from ward and reverse positions, a uid operated de.-

from and to a neutral position for controlling the -fluid supplied to said fluid operated means. and acting on said means` f or `controlling the iiuid device vcomprising a pair of servo valves, a casing movable with said device, and providing a relief passage for fluid acting on said device controlled by said servo valves, and a valve restricting the flow of fluid through said supply passage whenv the relief passage is open and operable when the relief passage -is closed to increase the pressure of fluid on.v said device. s

6. A uid operated servocontrol mechanism for a movably mounted element having, in combination, reversing means for moving said element in opposite directions froml a neutral position, a

member movable in onedirection from a neutral position and operable to control the position of said element on both sides of its neutral position, means forming a control piston operable to move said member towards its neutral position, means jfor supplying iluid under pressure continuously its neutral position "-d effective to determine the position of the element, means for supplying fluid under pressure to said iiuid operated means and said device, a reversing valve movable in opposite 'directions' from a neutral position for controlling the fluid supplied to said fluid operated means, means for controlling the fluid acting on said device comprising'a pair of servo valves, a casing for said valves movable with said device, a'.v uid f ment on both sides of its neutral position, means forming a control piston operable to move said supply passage to said device, and arelief passage in said casing for fluid acting on said. device controlled .by said servo valves, and a pressure operable valve -for restricting the ow of fluid through said supply passagel when said relief pas-y sage is open, .and operable When the relief passage is closed t'o increase the pressure of the iluid onsaid-device.

4. A fluid operated servo control mechanism for an element movable from a neutral position to selectablev forward and -revers positions, having, in combination, uid operated means for moving said element out of its neutral position, a i'luid operated device opposing the movement of the element from its neutral position, means for supi plying iluid under pressure to said fluid operated .i means and saidvdevice, a reversing valve movable to said piston to urge said member toward its l neutral position, and mechanism for controllingthe pressure of the uid acting on-the control piston comprising a servo valve, a casing movable with said member and having a port controlled by said servovalve, a reversingvalve for controlling' said reversingmeans, and means connecting the servo valve to the reversing' valve so that the servo valve operates for each direction of movement of said element. l

7. A nuid operated servo control mechanism for a movably 'mounted element having, in combination, means for moving said element in opposite directions from a neutral position, a member movable in one direction from a, neutral vposition and Voperable'to control the position of said elemember toward its neutral position, means including a control port for' maintaining fluid under pressure continuously on said piston to move said member toward its neutral position, and mechanism for controlling the pressure of the fluid acting on the control piston comprising a servo valve for controlling said port, a casing movable with said member as a unit0 and having said control port therein. a rotary reversing valve, andmeans connecting. the servo valve` to operate with the,

reversing valve.

8. A fluid operated servo control mechanism for an element movable from a neutral position f to selectable forward and reverse positions, having, incombinaton, a fluid. operated means foi` moving said element out of its neutral position from and to a. neutral position'for controlling the fluid supplied to said'uid operated means, a pair of servo control valves for controlling the pressure casing carried on said device and forming servo of the uid operating on said device and having av valve controlled ports. and means connecting said l servo valves to the reversing valve at points on opposite sides thereof when the reversing valve is in neutral.

5. A fluid operated servo control mechanism for an element movable from a neutral position'to -selectable forward and reverse positions, having,

in'combina'tion, a iluid operated means for moving said element out of its neutral position,a uid ""operated Y device opposing the movement of the element from its neutral position, means for supplying iluid under pressure' to said uid operaifedv I u l v l l w to forward and reverse positions, a fluid operated devicelopposing the movement of said eleable with said device and providingla s'ervo valve control port, an'd a link connecting said servo valve means to the reversing valve and in a dead vcenter position when the'reversing -valve is'in neutral;

9. A fluid operated servo control mechanism for an element movable 'from a neutral position to selectable forward andreverse positions, hav-h to forward and reverse positions, a fluid operated device opposing the movement of the said element from its neutral position and effective to determine the position of the element, means for supplying fluid under pressure to said fluid operated means and said device, a' rotary reversing valve movable in opposite directions from a neutral position for controlling the fluid supplied to said fluid operated means, a servo control valve for controlling the pressure of the fluid operating on said device and including a casing movable with said device and providing a servo valve control port, and means connecting said servo valve to operate with the reversing valve.

10. A fluid operated servo control mechanism for an element movable from a neutral position to selectable forward and reverse positions, having, in combination, a fluid operated means for moving said element out of its neutral position to forward and reverse positions, a fluid operated device opposing the movement of said element from its neutral position and effective to determine the position of the element, meansfor supplying fluid under pressure to said fluid operated means and said device, a rotary reversing valve movable in opposite directions from a neutral position for controlling the fluid supplied to said fluid operated means, and means for controlling the fluid acting on said device comprising a servo valve, a casing movable with said device having a relief passage for fluid acting on said device controlled by said servo valve, and a pressure operable -valve restricting the flow of fluid through said supply passage when said relief passage is open and operable when said relief passage is closed to increase the pressure of fluid .on said device.

l1. 'A fluid operated servo control mechanismv for a movably mounted element having, in combination, reversing means for moving said -element in opposite directions, a member operable to control the position of said element, means forming a control piston operable to move said .mem-ber, means for supplying fluid under pressure to said piston to move said member, mechanismfor controlling the pressure of the fluid acting on the control piston comprising a servo valve and a casing for a servo valve control port carried on said member and movable therewith as a unit and a reversing valve for controlling saidl reversing means.

12. A fluid operated servo control mechanism for a movably mounted element having, in combination, means formoving said element in opposite directions from a neutral position, a member movable in one direction from a neutral position and operable to control the position of said element on both sides oi' its neutral position, means forming a control piston operable to move said member toward its neutral position, means for supplying fluid under pressure continuously to said piston tormove said member toward its neutral position, 'and mechanism for controlling the pressure of the fluid acting 'on the control piston comprising a rotary servo valve having a contoured edge, av casingcarried on said member and movable therewith as a. unit and having a port controlled by said contoured edge, a rotary. reversing valve, and means connecting the servo valve to move 'withthe reversing valve.

13. ,A fluid operated servo control mechanism for a movably mounted element having, in coming, in combination, a fluid'operated means for .moving said element out of its neutral position ment in opposite directions from a neutral position, a member operable to control the position of said element on both sides of its neutral position, means forming a control piston operable to move Ysaid member, means including a control portI for maintaining fluid under pressure continuously on said piston to move said member in a direction to move said element toward its neutral position, and mechanism for controlling the pressure of the fluid acting on the control piston comprising servo valve means,la casing carried on said member and movable therewith as a unit and having said fluid port'gtherein and controlled by said servo valve means, and means including a reversing valve for controlling said reversing means.

14. A fluid operated servocontrol mechanism for a movably mounted element having, in combination, means for moving said element in opposite directions from a neutral position, a mem- Iber movable in one direction from a neutral position and operable to control the position of said element on both sides of its-neutral position, pressure fluid actuated means operable to move said member toward its neutral position, means for supplying fluid under pressure continuously to said fluid pressure actuated means to urge said member toward its neutral position including means forming a pair of ports movable with said member andthrough which the fluid flows alternately, mechanism for controlling the pressure of the fluid acting on said fluid pressure actuated means comprising a pair of servo valves each controlling one of said ports, a reversing valve for controlling said first mentioned means, and means connecting the servo valves to the reversing valve so that one servo valve operates for each direction of movement of said element.

15. A fluid operated servo icontrol mechanism for a movably mounted element having, in cornbination, means for moving said element in op- DOsite directions from a neutral position; a member movable in one direction from a'neutral position and operable to control the position of said element on yboth sides vof its neutral position, pressure fluid actuated means operable to move said memlber toward itsneutral position, means for supplying fluid under pressure continuously to said fluid pressure actuated means to urge said member toward its neutral position including means forming a portmovable with said member, mechanism for controlling the pressure of the fluid acting on said fluid pressure actuated means comprising aservo valve controlling said port, a reversing valve for controlling said first mentioned means, and means connecting the servo valve to operate with said reversing 'valve 16. A fluid operated servo control mechanism for a movably mounted element having, in combination, means for moving said element in opposite directions from a neutral position, a memb'er movable in one direction from a neutral position and operable to control the position of said `Vmemb fr toward its neutral position including ,means orming a port movable witlr said membination, reversing meansviorl moving said 'ee- 75;

'the fllli element on both sides of its neutral position, pressure fluid actuated means operable to move said member toward its neutral position, means for supplying fluid under pressure continuously to said fluid pressure actuated means to urge said ber, hanism for controlling the pressure of acting on said fluid pressure actuated means mprising a rotary` servo valve having a contour edge controlling said port, a revers.-

ing valve for controllingl said first mentioned means, and means connecting said servo, valve to operate with said reversing valve.

17. A fluid operated servo control mechanism for a movably mounted element having, in combination, means for moving said element in oppo-site directions from a neutral position, a member movable in one direction from a neutral position and operable to control the DOsition of said element on both sides of its neutral position, pressure fluid actuated means operable to move said member toward its neutral position, means for supplying fluid under pressure continuously to said fluid pressure actuated means to urge said member toward its neutral .position including means forming a port movable with said member, mechanism for controlling the pressure of the uid acting. on said fluid pressure actuated means comprising a rotary disk-like servo valve controlling said port, said valve having an intermediate peripheral portion adapted to be disposed in lcontrolling relation to said port when the valve i's in neutral position and non-.circular peripheral edges extending in either direction'from the intermediate portion,V

* unison.

18. A fluid operated servo control mechanis for a movably mounted element having, in combination, lmeans for moving said element in opposite directions'from a neutral position, a member movable in one direction from a neutral position and operable to control the position of said element on -both sides of its neutral position, pres sure fluid actuated means operable to move said 'member toward its neutral position,means for supplying fluid under pressure continuously to said fluid pressure vactuated means to urge. said member toward its neutral position, means for.

controlling the movement of said 'member 'bysaid pressure fluid actuated means comprising a servo 1 valve having a casing movable with-said member and provided with a iiuid control port a portion of'which extends substantially transversely to the Aline of movement of said member and a disk-like valve disposed at right angles to the transversely extending portionof said control port and having a non-circular peripheral edge controlling the ow of iiuid through said port, and a rotary4 reversing valve for controlling Vsaid first mentioned means disposed transversely of the line of movement of saidmember and parallel With the transverse portionl of said control port, said disklike valve being connected directly to said reversing valve to be rotatable therewith.

19. A fluid operated servo control mechanism for a movably. mounted element having, in combination, means for moving said element in opposite directions from a neutral position, a memmember toward its neutral position, means for the line of movement of said member. and a disk- 1 like valve disposed at right angles to the transversely extending portion of said control port and having an intermediate peripheral portion con- A forming tothe contour of said port and noncircular peripheral edges on either side of said intermediate portion; and a rotary reversing valve4 ,for controlling saidfflrst mentioned means disposed. transversely of the line of movement of said member and parallel 'with the transverse v portion of said'control port, said disk-like valve being .connected directly to said reversing valve to'be rotatable therewith GUNNAR. Awami/1an, 

